1. Field of the Invention
The present invention relates to photosensitive polymers, and the production of such polymers, and photoresist compositions that incorporate such polymers that can be used in the production of semiconductor and other microelectronic devices. The photosensitive polymers are prepared by a method of radical (cationic) polymerization from at least two monomers including a multi-ring alkenyl ether and an α-fluorinated acrylate, and may further incorporate one or more cyclic aliphatic and heterocyclic monomers and may be incorporated with one or more solvents, photoacid generators and organic bases to form photoresist compositions.
2. Description of the Related Art
As the manufacture of semiconductor devices becomes complicated and the integration density of semiconductor devices highly increases, there is a need to form a fine pattern. Furthermore, with regard to 1-Gigabit or more semiconductor devices, a pattern size having a design rule of 0.15 μm or less is needed. However, when a conventional photoresist material is exposed with KrF excimer laser (248 nm), there is a limitation in forming such a fine pattern. For this reason, development of a lithography technique using a new exposure light source, ArF excimer laser (193 nm), is under way to be commercially available in the near future. Also, for adoption to the manufacture of semiconductor devices in which formation of patterns of 0.15 μm or less is needed, research into another next-generation technique using F2 excimer laser (157 nm) as a new exposure light source is being extensively conducted.
Whereas research into ArF and F2 excimer laser techniques is being vigorously carried out, existing resist compositions suitable for use in those techniques cause many problems in practical use, compared to conventional KrF resist compositions.
Almost all well-known ArF resist compositions contain (meth)acryl-based polymers. Among these polymers, a methacrylate copolymer having an alicyclic protecting group, which is expressed by the formula below: 
This polymer includes an adamantyl group which tends to enhance the resistance to dry etching, and a lactone group, which tends to increase the adhesiveness, in its methacrylate backbone. As a result, the resolution of the resist and the depth of focus has improved. However, the resistance to dry etching is generally less than satisfactory for fine patterning processes and tends to result in serious line edge roughness in patterns formed from resist layers including such polymers. Another drawback of polymers having the formula above is that the raw materials used to synthesize the polymer is expensive.
As another conventional resist composition, a cycloolefin-maleic anhydride (COMA) alternating polymer having the following formula has been suggested: 
In the production of copolymer, such as a COMA alternating polymer having the formula above, resistance to dry etching is improved and the production cost of raw material is cheap, whereas resolution of the polymer sharply decreases. Also, the copolymer has a glass transition temperature (Tg) of 200° C. or higher due to the structural strength of norbornene contained in the backbone, resulting in processing difficulty. In addition, the synthetic polymers have in their backbone the alicyclic group, which shows prominent hydrophobicity, and thus the adhesiveness to neighboring material layers is very poor.
To overcome the described problems, in recent years, polymers having various structures have been proposed, the polymers exemplified by a copolymer of a COMA system and a monomer units having a (meth)acylate-based backbone: 
Since the copolymer having the above structure has a glass transition temperature (Tg) lower than that of the COMA system, the processing can be easily carried out. Also, since a polarity change occurs to (meth)acrylate monomer units, increased resolution can be achieved. However, according to reports hitherto made, resistance to dry etching has not been enhanced very much. To increase the resistance to dry etching, a bulky protecting group such as an adamantly group, rather than a t-butyl group, is introduced to the above structure. However, the resulting resist still exhibits weak resistance to dry etching or poor patterns.
As the pattern rule becomes finer in the manufacture of semiconductor devices, the aspect ratio is considerably increased, resulting in the collapse of patterns. To avoid this, a lithography technique using ArF excimer lasers may be used. However, in the case of using the lithography technique using ArF excimer lasers, patterns must be formed such that a resist layer is coated on a wafer to a thickness of 4000 Å or less. As the thickness of the resist layer is reduced as above, it is necessary to enhance resistance to dry etching.
Another conventional resist composition proposed for enhancing resistance to dry etching includes a polymer having only a norbornene structure in its backbone, represented by the following formula: 
Photoresists incorporating such polymers, however, tend to be hydrophobic, suffer from reduced adhesion and exhibit reduced transmittance, reducing their utility for forming fine patterns. Further, in order to obtain the above structure, a catalyst including a heavy metal such as platinum or nickel is necessary to induce the desired polymerization. However, a portion of the heavy metal catalyst remains in the resulting polymer product even after purification. As a result, photoresist compositions incorporating such polymers present a serious risk of heavy metal contamination and would not be practical for use in most semiconductor process applications.
Other conventional photoresists have included copolymers of norborene and tetrafluoroethylene as represented by the formula: that tend to exhibit improved transmittance as a result of the additional fluorine in the main chain, but also tend to have poor adhesion characteristics. Other photoresists have incorporated more highly fluorinated polymers that may be represented by the formulas: to provide additional improvements in transmittance, but these improvements tend to come at the expense of reduced resistance to dry etch processes and/or reduced adhesion.